Dark side

Since the Moon's rotation around its axis is equal to its orbital period, or the time it takes the Moon to travel around Earth, the same side always faces Earth. While scientists have studied samples from the Moon's near side, the far side and its polar regions have remained in the dark.

For instance, the lunar south pole sits in the solar system's largest crater, called the South Pole-Aitken Basin, which is 1,616 miles (2,600 kilometers) across and 7.5 miles (12 kilometers) deep. SMART-1 snapped loads of photos of the crater, while gathering chemical data. With such depths, the scientists hope to get a peek at the Moon's mantle layer, just beneath the crust. The theory is, if the Moon accreted material over time, the deeper you go the further back in time you go.